A transparent base material such as glass and plastic causes dew condensation at its surface due to the differences of temperature and humidity between the inner surface and the outer surface of the base material such that the water content in the atmosphere is adhered to the surface of the base material with its form changed into waterdrops, the differences being caused in the case where the temperature of either one of the surfaces falls below the dew point or in the case where an abrupt change of temperature and humidity occurs on the base material (e.g., in the case where the boiling steam is in contact with the base material, in the case where the base material is moved to a hot and humid environment from a cold portion, and the like). As a result of this, light scattering due to the condensed waterdrops, i.e. so-called “hazing” is caused, and so the visibility is impaired. With this “hazing”, glasses for general use such as window glass, showcase glass, front glass for automotive vehicle or airplane, mirror, eyeglasses, sunglasses and the like are far reduced in safety and viewability.
As a method for imparting antifogging property to these base materials, there is a method of forming a coating film having hydrophilicity and water absorbing property. For example, in Patent Publication 1, there is disclosed a curable resin composition for antifogging coating, containing as essential components: (A) a carboxyl group-containing hydrophilic polymer having a number-average molecular weight of 5,000-20,000 composed of 50-100 wt % carboxyl group-containing unsaturated monomer and 0-50 wt % other copolymerizable hydrophilic unsaturated monomer; and (B) a hardener containing three or more epoxy groups in a molecule and having a water-dissolution ratio of not less than 50 (which is defined by multiplying an actually dissolved parts by weight when dissolving 10 parts by weight of the hardener in 100 parts by weight of water at room temperature by 10). As examples of other copolymerizable hydrophilic unsaturated monomer, Patent Publication 1 cites ethylene glycol mono(meth)acrylate, diethylene glycol mono(meth)acrylate, propylene glycol mono(meth)acrylate, dipropylene glycol mono(meth)acrylate, triethylene glycol mono(meth)acrylate, tripropylene glycol mono(meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate and polyethylene-propylene glycol mono(meth)acrylate, methyletherification products of these and the like.
Additionally, Patent Publication 2 discloses an antifogging coating composition containing: (A) 40-70 parts by weight of copolymer consisting of 50-80 wt % alkylene structural unit having an amide bond at side chain and 20-50 wt % alkylene structural unit having —C(═O)—O—X (where X represents a hydroxyl group-containing organic group) at side chain; (B) 30-60 parts by weight of polymer or copolymer containing at least 20 wt % alkylene structural unit having —C(═O)—O—Y (where Y represents an epoxy group-containing organic group) at side chain (100 parts by weight of the total of (A) and (B) is the primary component); an epoxy group-containing organic silane compound and/or melamine skeleton-containing compound (as an accessory component) in an amount of 0.3-30 parts by weight relative to 100 parts by weight of the total of (A) and (B); and further a curing catalyst. As examples of a vinyl monomer that provides the alkylene structural unit having —C(═O)—O—X (where X represents a hydroxyl group-containing organic group) at side chain, there are cited hydroxyethylacrylate and methacrylate, 2-hydroxypropylacrylate and methacrylate, and polyethylene glycol methacrylate and acrylate.
Additionally, Patent Publication 3 discloses an antifogging agent containing a water-absorbing polymeric compound and a cross-linking agent and capable of being applied and cross-linked on target articles thereby preventing the target articles from the clouding due to moisture. As examples of the water-absorbing polymeric compound, there are cited an acrylic copolymer containing carboxylic acid or salts thereof, an olefinic copolymer containing primary amino groups or salts thereof, an olefinic copolymer containing secondary amino groups or salts thereof and the like. As the cross-linking agent, an epoxy cross-linking agent is cited.
Furthermore, there is set forth in Patent Publication 4 an antifogging article comprising a base material and a water absorbing crosslinked resin layer formed on the surface of the base material, the antifogging article being characterized in that the water absorbing crosslinked resin layer is a crosslinked resin of 45 mg/cm3 or greater saturated water absorption. Additionally, it discloses that the crosslinked resin layer is formed by reacting a cross-linkable component and a curing agent.